Development of an energy filtering direct electron detector for diffraction studies in the SEM

  • Stefano Vespucci

Student thesis: Doctoral Thesis

Abstract

This thesis describes the application of an energy filtering digital direct electron detector for diffraction studies of materials in the field emission scanning electron microscope (SEM). The main aim was the development of the digital complementary metal-oxide-semiconductor hybrid pixel detector, \Timepix" for electron backscatter diffraction (EBSD), a technique which allows the acquisition of precise crystallographic information from the surface of a sample, such as crystallographic orientation, phase and strain. EBSD results from nitride semiconductor, silicon and diamond thin films and tungsten-carbide cobalt samples are presented and used to illustrate the advantages of acquiring EBSD patterns with the Timepix detector, in particular to demonstrate the improvement in the contrast and increase in the detail contained in the EBSD patterns as consequence of the energy filtering. Alongside EBSD, new applications were developed such as re ection high energy electron diffraction (RH EED) in the SEM. RHEED is a very surface sensitive technique which in principle could allow the study of ultrathin samples where conventional SEM based methods are limited. The combination of RHEED and Kikuchi diffraction, led furthermore to the development of surface wave resonance electron channelling contrast imaging (SWRECCI), which allows crystalline defects such as surface steps, grain boundaries, dislocations and stacking faults to be imaged with a high level of surface sensitivity, iii extending furthermore the application of ECCI to non-continuous surfaces. This is obtained by selecting experimental geometries which stimulate the surface wave resonance at the specimen surface. Transmission diffraction in the SEM was also explored, resulting in the acquisition of transmission diffraction patterns and in the generation of images of the sample obtained under experimental conditions analogous to scanning transmission electron microscopy. This allowed for example, bright anddark f ield images of the specimen to be obtained. The resulting images exhibited crystalline contrast not often observed in the SEM. The Timepix sensor is constructed from a piece of single crystal silicon. Diffraction effects within this single crystal were found to result in the Timepix detector response exhibiting an underlying diffraction pattern; that is a detector diffraction pattern (DDP). The DDP provides a watermark from which the location of the camera relative to the position of the electron beam on the sample may be precisely and accurately determined. This opens up new opportunities for improved mapping of the strain distribution in materials for example. The development of all the novel techniques summarized above opens up new horizons which need to be explored.
Date of Award7 Jun 2018
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SupervisorCarol Trager-Cowan (Supervisor) & Paul Edwards (Supervisor)

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